Shadow

Shadow, reduction of light on an area caused when an opaque object interrupts the light source. The shadow appears on the side of the body away from the source; the brighter the light, the darker and crisper the shadow seems. A very dark shadow, called an umbra, occurs when the light is completely obstructed. A lighter area surrounding the umbra, called the penumbra, occurs when the light source is larger than the interrupting object, allowing some light to shine beyond it.